Increased daytime naps, and increased fragmentation of nocturnal sleep, occur with aging. Yet there have been no systematic studies of the effects of naps on subsequent nocturnal sleep, sleep satisfaction or mood in the elderly. This limits our ability to make rational prescriptions for sleep hygiene. We have shown in young adults that the timing of naps differentially affects the architecture of post-nap night sleep: naps taken at 3 PM or earlier reduce computer-measured delta only in the first NREM period whereas later naps alter the clinical effects of naps. We have shown further that delta occurring in daytime naps is homeostatically "subtracted" from post-nap night sleep. Current models hold that NREM delta is the "recuperative" component of sleep homeostasis. The research proposed could lead to the simplest, least arduous and least expensive clinical test of delta homesostatasis. The proposed studies will also determine whether the rate of delta accumulation with increasing waking follows an exponential or logistic (growth) model. This distinction can guide hypotheses regarding the biology of delta homeostasis and also permit more precise quantitative models of sleep-waking relations. The scientific yield of these studies will be enhanced by: application of both spectral (FFT) and period-amplitude analysis to the digitized data, precise measurement of gender effects in young adults and elderly; measurement of delta-sigma and delta-beta oscillatory relations in the elderly; and an experimental test of the hypothesis that REM latency, the most heavily studied component of sleep in psychiatric patients, is substantially determined by delta pressure.